Rectifying apparatus



June 1.4, 1932 M, A. LlssMAN RECTIFYING APPARATUS Filed Jan. 11, 19:50:s sheets-sheet INVENTOR.

A TTORNEYS June 14, 19,32- M. A. LlssMAN RECTIFYING APPARATUS Filed Jan,11. 1930 3 Sheets-Sheet 2 A TTORNEY June 14, 1932. M, A. LlssMAN1,862,936

RECTIFYING APPARATUS Filed Jan. ll, 1930 3 Sheets-Sheet 3 N VEN TOR. v/Wafce/ asma/7.

AT 0RNEY5 l ance in the reverse direction.

Patented .June 1.4, 1932 UNITED STATES PATENT OFFICE MARCEL A. LISSHAN,F LOS ANGELES, CALIFORNIA, ASSIGNOR TO INTERNATIONAL PRECIPITATIONCOMPANY, OF LOS ANGELES, CALIFORNIA, A CORPORATION OF CALIFORNIARECTIFYING APPARATUS Application filed January 11, 1930. Serial No.420,130.

This inventionrelates to apparatus for rectification of alternatinelectric current, and particularly to rectifying apparatus of theasymmetric film type, such as the well known copper-copper oxiderectifier. Such rectifiers depend upon,l the asymmetrical conductivityof the surface between two closely contacting members, for examplebetween a plate of copper Land a layer or film of cuprous oxide formedthereon, in vwhich case the resistance to flow of electric current fromthe/oxide to the copper is many times less than the resist- The voltagewhich ma be impressed across one such asymmetrically conductiveinterface without causing rupture or breakdown thereof is ordinarilyrelatively small, for example on the order of from 1 to 10 volts, but byconnecting a suitable number of elements in series, any desired voltagema be handled satisfactorily.

The principal o ject of the present invention is to provide a rectifierconstruction which permits a large number of asymmetric solid contactrectif ing elements to be assembled in a relatively s ort space and inseries connection with 'one another, and which provides a maximum areaof the asymmetrically conductive surface, such as the surface betweenthe copper andthe oxide coating, of each element.

A further object of the invention is to provide a construction adaptedfor rectification of relatively small electric currents at relativelyhigh total voltage, in an apparatus of moderate sizeand low cost ofmanufacture and assembly.

- A further object of the invention is toprovide a simple andinexpensive means of aslselnbling suitable numbers of such rectifyingelements to form units of convenient size, and novel means for mountingand interconnecting such units.

A common typel of copper oxide rectifier l .construction heretoforeemployed vconsists of a plurality of spaced apart copper discs or plateshaving an oxide coating or film on veach face thereof, metal contactplates held in contact with the copper oxide coating at the respectivesides of eachcop er plate, and separate connecting members or connectingeach copper plate to the contact plates of an adjacent element, wherebythe desired number of said elements are connected in series. In thisform of construction the elements are ordinarily separated by air gapswhich permit dissipation of heat to the air therebetween,

tion is not well adapted to the rectification of l relatively highvoltages where a large number of elements must be connected in series.Furthermore, when the current to be conducted is relatively small, theheat dissipation requirements are much less and the spaced apartarrangement of the elements is not required.

Another type of construction which has been heretofore used comprisesmerely a stack of copper plates, each coated with copper oxide upon onlyone face, with alternate contact plates, such as lead washers,interposed ,therebetween, and an insulated bolt or other compressionmember extending longitudinally through the centers of all of theelements and serving to hold the same in tight engagement, with therespective contact plates establishing contact between the severalcopper plates and the oxide coatings of the adjacent plates. Onedisadvantage of this latter construction, however, is that each copperample, a series of oxide-coated copper plates in close proximity to oneanother and without intervening air spaces, while at the same timepermitting the use of plates coated with copper oxideover the majorportion of both faces thereof, but with suitable provision forconnection from a relatively small non-oxidizved surface portion .ofeach plate to substantially the entire surface of the oxide coat-` 1`,ing oi thenext plate, thus providing a relatively great number ofelements in a given len h and at the same time providin for uti izationof the maximum asymmetrically conductive surface per element. l

A preferred embodiment of rectifying apparatus of my invention, by meansof which the above objects are accomplished, comprises essentially apluralit of copper plates arranged in a stack an each having a coa-tingof cuprous oxide formed thereon in any suitable manner and extendingover the major portion of both faces thereof, corresponding contactelements consisting preferably of soft metal foil, each of said contactelements extending over and in intimate Contact with substantiall theentire surface of the oxide coating at oth sides of the correspondingcopper plate and also having a portion. extending in intimate contactwith a nonoxidized surface portion oi relatively small area on anadiacent copper plate, suitable insulating means interposed lie-tweenthe overlapping portions of the adjacent contact elements, and meanscompressing the entire stack so as to maintain tight engagement andintimate electric Contact of the Contact elements with the oxidized andnon-oxidized surface portions of the copper plates. llt will be seenthat this construction ltakes advantage of the act that the conductivityfrom the nonoxidized portion of the copper plate to the metallicconducting element in contact therewith is much greater than theconductivity between the copper oxide coating andthe cop er plate, evenin the direction of relative y high conductivity, so that a contact ofthe contact element with a relatively small non-oxidized surface portionis capable of handling the saine current ilow as may be passed throughthe relatively large area of surface between the copper oxide film andthe copper.

llt will he understood that other asymmetrically conductive solidcontact rectifying elements may also be mounted and assembled in asimilar manner, such as silversilver oxide elements, elements eachcomprising a plate of aluminum having n coating of sulphide thereon and'a layer of cupric sulphide in contact therewith, or elements consistingof aluminum in Contact with cuprous sulphide, However, for the sake ciclarity, the following description will be directed particularly torectifying apparatus of the copper-copper oxide type, it beingunderstood that this is by way of example only.

The apparatus also comprises certain novel means for mounting the'stacks of rectiying elements above described so as to form units ofconvenient size, and novel means for assembling and interconnectingthese units, as hereinafter described.

35 The accompanying drawings illustrate emhodiments of my invention andreferring thereto:

Fig. l is a vertical section on line 1 1 in Fig. 2, showing anintermediate stage in the assembly of a stack of copper-copper oxiderectiiying elements according to my invention.

Fig. 2 is a side elevation taken from the left side of Fig. 1.

lF ig. 3 is an inverted plan view of lF ig. 2, showing the manner ofinserting the next copper plate in the stack.

Fig. 4 is a longitudinal section of a partly hroken away stack ofrectifying elements.

Fig. 8 is an end view from the left end of I la ig. 9 is a sideelevation showing a l lurality` of units connected in series an eachcomprises a plurality of stacks also connected in'scries.

Fig. l0 is a horizontal section on line :io-10 in rig. e.

Fig. il is a vertical section on line ll-il in Fig. 9.

it should be stat/ed, at the outset, that in certain iigures of thedrawings the rectifying elements, the Contact elements and theinsuloting and spacing means are exaggerated in thickness, in proportionto their other dimensions, in order to show the shape and positionsthereof more clearly. Also, in' .certain igures some or all oi theindividual recti ing elements are not indicated, as this woul involve aneedless repetition oi parts.

Referring to Figs. 1 to 3 inclusive, l have indicated at 2 an end plate,preferably oi rectangular shape, and consisting of copper `or an othersuitable metal or conducting material, while the first rectifyingelement is indicated at la. Said iectifying element is shown ascomprising a. copper plate 3, preferably of rectangular shape andprovided with a coating oi cuprous oxide formed thereon in any suitablemanner and extending over the entire contacting area of one face, asindicated at e, and over the maior portion of the other face, asindicated at 5. A relatively small portion or" this last mentioned face,however,l is free from copper oxide coating, as indicated at 6, thefreedom from oxide coatin over this portion of the plate being securedin any suitable manner, as, for example, by first coating the entireexterior surface of the plate and then removing the oxide coating fromthis face of the plate above thepoint indicated at 7. Contact from theend plate 1 to the copper oxide coatings 4 and 5 over the major portionof the surface of both sides of the copper plate 3, is rovided by meansof a sheet of soft metal il having a portion 8 lying between said endplate and the oxide coating 4, and bent in U-shape, and having the otherside of the U extending, as indicated at 9, in contact with oxidecoating up to adjacent the upper edge 7 of said coating.

The contact element 10b for establishing connection between the uncoatedportion of the copper plate 3 and the copper oxide coatin of the nextplate is-shown as also comf prisin a sheet of thin soft metal foil, suchas lea foil, also bent in U-shape, with the two arms of the U, indicatedat 11 and 12 respectively, connected together by a web portion 13 andspaced apart sufficiently to receive the next rectifying element 1btherebetween, as shown in Fig. 3, said contact element also including aportion 14 bent over at one side of the portion 11 and engaging aportion of the exposed surface 6 of the copper plate of the firstrectifying element 1a. Between the overlapping portions of the metalfoil Contact strips 9 and 11, there .is interposed a sheet of insulatingmaterial 16 consisting,

for example, of paper or the like of sufficient thickness and dielectricproperty to serve as an effective insulation against the potentialdifference between the. adjacent rectifying elements. Also, in order tocompensate for the absence of the copper oxide coating between theportion 14 of the contact element and the copper plate, suitable fillingmeans is interposed behind said portion. For example, the insulatingstrip 16 may extend up behind the portion 14, and a filler or strip 18of suitable material, such as paper or the like, may be placed betweensaid lnsulating strip and said portion 14, said filler being ofsubstantially the same thickness as the copper oxide coating, so thatupon application of pressure to the stack of rectifying elements, saidportion 14 will be pressed into tight engagement with the copper plate.

For the purpose of clearly illustrating the principle of this invention,reference may now be had to one of the stacks of rectifying elementsshown in Fig. 6. In this figure the layers of insulating and fillingmaterial are omitted, in order to show more clearly the relativepositions of the copper plates and the metal foil contact elements. Anydesired number of rectifying elements, such as indicated at 1a, lb-l,may be assembled in the above described manner so as to form a stack ofconvenient length. The bare surface portion 6 of the last element is inturn connected l by a metal foil contact element having a portion 21 incontact with the non-oxidized surface portion 6 of said rectifyingelement and a portion 22 making Contact with the inner face of anotherend plate 2. Referring to the uppermost stack lof rectifying elements D1in Fig. 5, it will be seen that electric current will be permitted topass therethrough substantially only in the direction indicated by thearrow applied thereto. Suchl current enters through the end plate 2,passes through the portions 8 and 9 of the first Contact element to thecopper oxide film indicated at 4 and 5, through said film to the copperplate 3 of the first element, thence through portion 14 of contactelement 10b tothe copper oxide film of the next element 1b, and so onthrough all of the elements of the stack in series. The voltage whichmay be impressed across such a stack of rectifying elements withoutcausing breakdown of the film of copper oxide at' an point is a functionof the permissible vo ta e drop across each film and the number 0%elements in the stack. v

While the construction ,of my invention is intended particularly for usewith relatively small electric current flow, there will nevertheless bea. certain amount of heat produced upon passage of current therethrough,and in order to facilitate dissipation of such heat and preventover-heating of the elements I prefer to rovide each of the copperplates with a projection or fin 24 projecting at least one side beyondthe cross section of the stack proper, that is, beyond the area coveredby adjacent contact elements. In Fig. 5, for the sake of clarity, I haveshown these projecting fins 24 as all extending in the same directionfrom the stack, and it will be understood that it is within the scope ofthe invention to use such a construction.- However, in order to increasethe clearance between adjacent proj ections and. thus increase theopportunity for dissipation of heat therefrom, I prefer to mount eachcopper plate with its projection extending in a different direction fromthe projectionof each adjacent plate. A part1c ularly advantageousconstruction is the one illustrated in Fig. 4, in which end plate 2 hasa projection 25 extending downwardlyz while the first rectifying plate1a has its projection (not shown) extending at right angles to theprojection 25, that is, either forwardly or rearwardly with respect tothe plane of the drawings, the next rectifying plate 1b has itsprojection 24 extending upwardly, the next plate 1e again has aprojection extending either forwardly or rearwardl and o poslte to theprojection of plate 1a an so on t rough the series. The other end late2', in turn, has its projection 25 exten ing at right angles tothat" ofthe last preceding rectifymg element. At any one side of the stack,therefore, the successive projections are separated by adistance equalto four times the interval between adjacent rectiying elements, thusproviding amplespace for circulation of air or other cooling mediumbetween these projections'to eiiect dissipation of heat therefrom.

ln the particular construction shown, this angular displacement of thecooling fins of the successive rectitying elements is brought about byforming each of the contact elements with its bent over portion 14connected to one of the edges of the portion 11 which isadjacent to theweb 13, so that when such contact element is placed in proper relativeposition with respect to the receding contact element, such elements areisposed at right angles to one another. -Each rectiiving element isplaced with its extension 24 projecting out through the open side oi theU of the corresponding contact element. thus causing the projections ofthe successive elements to be also disposed' at right angles to oneanother. lt will beunderstood. however, that this construction may bemodiiied without departing from the invention.

All of the rectiying eiements and contact elements of each stacl may becompressed by any suitable means so as to cause intimate contacttherebetween. ln Figs. 4 and 5., the compressing means is shown ascomprising thrust means such as bars 27 engaging insulating plates 28which in turn engage the outer faces of the end members 25 and 25, andbolt 29 and nut 31 serving to draw said thrust members toward oneanother and exert the desired compression upon the stack, so as to forcethe soft metal contact elements into intimate contact with the oxidizedand nonoxidized surface portions of the copper plates.

ln Fig. 4, the contact elements 10b, etc. and the insulating means 16and 18 are 'also shown in their proper relative position between therectifying elements, and it will be evident that, upon tightening nut31, the entire stack may be compressed 'suinciently to cause intimateconductive contact between substantially the entire area of the portions11 and 12 ot each contact element and the oxide-coated surfaces 4 and 5of the corresponding rectitying element, and also be- -tween the portion14 thereof and the nonoxidized surface portion 6 o the next recti-.fying element.

As shown in Fig. 5, a number of stacks, in`

' neeaese cent stacks. Furthermore, if desired, additional ide meanssuch as insulating sleeves 34 hel in position by bolts 35 may beprovided between the stacks, and similarly engaging therewith, wherethere are no compressing bolts 29.

Electrical connection to the opposite ends 1 of each stack and betweenthe successive stacks when a plurality thereof are to be connected inseries may be provided in any suitable manner. ln Figs. 4 and 5, forexample, the projections 25 and 25 of the respective end members areshown as provided with connecting lugs or terminal pieces 36 forconnection ot suitable electrical conductors thereto. ln Fig. 5 thestacks D1L and D2 are shown as connected in series by means of wire 37connecting together the terminal pieces 86 at the adjacent ends thereof,it being understood that when connected in this manner the rectifyingelements of the respective stacks should be reversed in position so asto permit iow of current in one direction in the stack D1 and in thereverse direction in the stack D2, for example as indicated by thearrows applied thereto.

Fig. 6 illustrates an arrangement of four stacks of rectifying elementsD1, D2, D3 and ll)4 for full wave rectification at moderate voltage.rlhe rectifying elements in stacks D1 and D, are so disposed as topermit assage of current only toward the left, W ile the rectifyingelements in stacks D2 and D8 are so disposed as to permit passage ofelectric current only toward the right, as indi cated by the arrowsapplied to the respective stacks. Two alternating current supply wiresare indicated at 41 and 42, one of said Wires being connected by wires43 to the adjacent end members 2 and 2 of stacks D1 and Dz'respectivelyand the other of said Wires being connected by wires 44 to the adjacentend members 2 and 2 of stacks D3 and D, respectively. At the other end,the end lates 2 of stacks D2 and D8 are connected y wires 45 to a commonoutput wire 46, While the end plates 2 of the remaining stacks D1 and D4are connected by wires 47 to the other output wire 48. Upon applicationof alternating current of suitable voltage to the wires 41 and 42,direct current will be `delivered through the wires 46 and 48 to anysuitable load which may be connected therebetween, the oppositelydisposed stacks of rectifying elements acting in the usual manner offull wave rectifying systems. wave the current will flow from wire 41through stack D2 to` wire 46 and back through wire 48 and stack D4 tothe wire 42,

-and during the next half-wave the current will iow from wire 42 throughstack D3 to Wire 46 and back through Wire 48 and stack D1 to wire 41.

A simplemeans of mounting four stacks of rectitying elements connectedfor full wave During one halfl rectification as above described, isshown in Figs. 7 and 8. In this case the four stacks of rectifyingelements are compressed by means of end members 51, each provided withfour arms 52 engaging the ends of the respective stacks, and by means ofbolt 53 and nut 54 serving to draw said end plates toward one another.Suitable insulating members 55 are mounted between the end plates 2 and2 of the respective stacks and the arms 'of the thrust plates. Inthis-case the end plates 2 and 2 of stacks D1 and D2 are shown asconnected together by a web plate 56, preferably formed integrally withsaid end plates. In a similar manner web plate 57 connects together theend plates 2 and 2 of stacks D3 and D2, while at the other end the endplates 2 of stacks D2 and D3 are connected together by web plate 58 andthe en plates 2 of stacks D1 f1nd D4 are connected y web plate 59.Suitable means such as binding posts 61 are mounted on the respectiveconnecting members 56, 57, 58 and 59, for connection thereto ofelectrical input and output conductors corresponding to the wires 41,42, 46 and 48 respectively of Fig. 6.

In Figs. 9 to 11 inclusive I have illustrated a type of rectifying unitprovided with a plurality of stacks of rectifying elements all connectedin series, and a simple means of mounting a number of such units forconnection of all of the units in series, for the purpose ofrectification at relatively, high voltages. In this case each unit isshown as comprising three stacks of rectifying elements of the abovedescribed construction, indicated at F1, F2 and F3 respectively, saidstacks being compressed into tight contact throughout by means ofthree-armed thrust plates 65, insulated from the ends of the stacks byinsulating plates such as above described, and

held together by bolt 66 and nut 67 engaging.

the outer faces of the respective thrust plates. An advantage of thisform of the invention is that the three point engagement of the thrustplates with the ends of the group of stacks insures that thrust plateswill bear with equal pressure against the ends of all of the stacks, andthus provide tight compression in all of the stacks, due to the -abilityof said thrust plates to tilt slightly in 'any direction to compensatefor slight dierencesl in the length of the several stacks. Bolt 66 isshown as provided at each end with a threaded extension 68, which mayadvantageously be of reduced diameter, and upon each of said extensionsa metal contacty sleeve 69 is secured by means of nut 71, said sleevebeing completely insulated from the bolt, as, for example, by means ofinsulating bushing 72 and insulating washers 73 and 74.

Each contact sleeve 69 is shown as provided with a connecting lug 76projecting outwardly therefrom.

Two of the 'stacks such as F1 and F 2 are shown as having their elementsso arranged as to provide for How of current therethrough in the samedirection, while the third stack such as Fig. 2 has its elementsdisposed so as to provide for flow in the reverse direction, asindicated by the arrows in Figs. 9 and 10. The connecting lug 76 at oneend is connected by wire 77 to a connecting lu 78 on the adjacent endmember of the stac F1, while the connecting lug 76 at the opposlte endis connected by wire 79 to a similar connecting lug on the adjacent endmember of stack F 2. The ends of the stacks F1 and F3 opposite the endsto which are connected the wires 77 and 79 respectively, are connectedto the adjacent ends of the stack F2 by any suitable means such as smallconnecting webs, one of which is indicated at 81 in Fig. 11, saidconnecting webs being preferably formed integrally with the end plates.It may be seen, therefore, that all of the rectifying elements of all ofthe stacks of each unit are connected in series between the contactsleeves 69 at the opposite ends thereof. For example, from the contactsleeve at the left of unit shown in Fig. 10, the current may ow throughwire 77 and stack F1, thence through the connecting member (not shown)to the stack F2 and through said last named stack, then through theconnecting member 81, to the stack F2 and through the stack F2 and wire79 to the contact sleeve at the other end of the unit.

The rectifying units are shown as mounted on upright supporting strips83, preferably formed of insulating material. Said units may be mountedon said supportingstrips in any suitable manner, for example by means ofcontact clipsV 84 in which the contact sleeves of two adjacentrectifying u nits may be removably inserted. Each of said clips is shownas comprising a flat platev portion 85 mounted upon the strip 83 bymeans of screws 86 and provided at each end with two resilient arms 87having suitably curved portions forming a socket in which the contactsleeve 69 is adaptedto be inserted by'pressing the same inwardlywhereupon it will be resiliently held between said arms. Thisconstruction provides therefore, not only for supporting the rectifyingunits but also electrically connecting adjacent units in series. Forexample, in Fig. 9 the rectifying units indicated at K are shown asform. ing part of a horizontal row of units all connected in series,while the units K are shown as forming part of another row connected inseries. In assembling large numbers of units of this type, alternaterows may advanta-- geously be mounted on opposite sides of thesupporting strips 83, as shown in Fig. 11, in'

order to conserve space by permitting the rows to be spaced as closetogether vertically as possible. By thus mounting and properlinterconnecting a sucient number of suc recti ing units, rectication ethigh voltage electricity may be obtained for any desired purpose, forexample for the energization of electrical precipitation apparatus orother apparatus where high voltage unidirectional current is required.Advantages of this form of rectifying means when used for such and alsohaving a non-oxidized contact surface portion of relatively small area,a plurality of metal contact elements correspond ing to the respectivecopper plates and each making Contact with substantially the entiresurface of the copper oxide coating on both faces of one of said copperplates and having a portion also interposed in the stack and makingContact with the non-oxidized surface portion of an adjacent copperplate, insulating and spacing means interposed between adjacent copperplates and contact elements in such manner as to provide a compact stackadapted to transmit pressure throughout its length, and meanscompressing the entire stack longitudinally so as to hold the contactelement-s, solely by the pressure thus exerted thereon, in intimatecontact with both the copper oxide coatings and the non-oxidized surfaceportions of the copper plates.

2. An electric current rectitying apparatus as set forth in claim 1,each or said copper plates being provided with a portion projecting fromone edge thereof beyond the cross section of the stack to serve as a;cooling fin, and the fins on adjacent plates projecting in differentdirections so as to increase the space therebetween.

3. An electric current rectifying apparatus as set forth in claim l,said means compressing the stack comprising thrust members engagingtheoppositeends of said stack and means extending outside thecross-section-ot the stack and holding said thrust members toward oneanother.

4. An electric current rectitying apparatus comprising a plurality ofcopper plates arranged in a stack and each having a coating of copperoxide formed over substantially the entire area of one contact facethereof and over the major portion of the other contact face thereof, avrelatively small surface portion or said other face of each plate beingfree of copper oxide coating, a plurality of Lacasse metal contactelements interposed between the respective copper plates and each havinga U-shaped portion making contact with substantially the entire copperoxide coating on both contact faces of one of said plates and a portionbent over at one side of said lil-shaped portion and making contact withthe uncoated surface portion of an adjacent plate, and means comprisingthe entire stack so as to maintain intimate contact between the saidportions of the contact elements and the copper oxide coatings and theuncoated surface portions of the copper plates.

5. An electric current rectify/ing apparatus comprising a plurality ofsubstantially rectangular copper plates arranged in a stack and eachhaving a coating of copper oxide formed over substantially the entirearea of one contact face thereof and over the maj or portion ofthe othercontact face thereof, said other Contact tace having a relatively smallportion of its surface non-oxidized, a plurality of contact elementsinterposed between the respective copper plates and each having aU-sbaped portion one arm of which makes contact with substantially theentire area of the first-named contact tace of one of said plates andthe other arm or" which makes contact with substantially the entireoxide-coated portion of the other contact face of the same plate. andalso having a portion bent over at one edge of the first-named arm ofthe U-shaped portion and making contact with the non-oxidized surfaceportion of the next copper plate, and means compressing the entire stackso as to maintain intimate contact between the contact elements and thecopper plates.

6. An electric current rectifying apparatus as set forth in claim 5, andcomprising in addition insulating members interposed between theoverlapping portions of the adjacent contact elements.

7. An electric current rectifying apparatus as set forth in claim 5, andcomprising in addition filling means between the nonoxidized surfaceportion of each copper plate and the next plate. ot sufcient thicknessto compensate for the absence ot the copper oxide coating and maintaintight engagement of said non-oxidized surface with the corresponding`contact element under the pressure caused by said compressing means.

8. An electric current rectifying apparatus comprising three stacks ofasymmetric solid contact rectifying elements, each of said stackscomprising a plurality of such rectifying elements and a plurality ofcontact elements connecting said rectifying elements in series :forpassage of electric current in substantially one direction only throughthat.

entire stack, the elements of two of said stacks being disposed so as topermit current iow in a direction reverse to the dow oit current in Vthethird stack, common thrust members engaging the opposite ends of all ofsaid stacks and freely movable into tight three-point engagementtherewith, compressing' means extending outside the cross section ofsaid stacks and holding said thrust members toward one another so as totightly compress the stacks and maintain tight contact between therectifying elements and contact elements throughout each stack, meanselec trically connecting one end of said third stack to the adjacent endof one of said two stacks, and means electrically connecting the otherend of said third stack to the adjacent end of the other of said twostacks so as to connect all of said stacks in series with one another.r.

9. An electric current rectifyin apparatus comprising a plurality ofrecti ying units, each of said units' comprising three stacks extendingside by side and each stack comprising a plurality of asymmetric solidcontact rectifying elements and a plurality of `contact elementsconnecting said rectifying elements in series for passage of electriccur.-

rent in substantially one direction. only through the entire stack, eachof said rectifying units further comprising means electricallyconnecting all of the stacks of rectifying elements of said units inseries, common thrust members engaging the opposite ends of all thestacks of said units` compressing means extending' outside the crosssection of said stacks and holding said thrust members toward oneanother so as to tightly compress the stacks and maintain tightelectrical contact between the rectifying elements and contact elementsof each stack, contact members at the opposite ends of said unit andmeans electrically connecting the respective contact 40 members to theopposite ends of the series of stacks of said unit, and said apparatusfurther comprising supportingl means, and connecting clips mounted onsaid supporting means and provided with means for removably receivingthe contact members of two adjacent rectifying units, said rectiyingunits being mounted with the adjacent connecting members of adjacentunits removably inserted in the respective connecting clips` 50A wherebysaid clips serve both to support said units and to electrically connectall of said units together in series.

In testimony whereof I have hereunto subscribed my name this 2nd day ofJanuary,

MARCEL A. LISSMAN.

